EPR study of highly stable methyl radicals trapped in synthetic H-rho zeolite

Abstract

Methyl radicals generated by ă-irradiation in the proton form of synthetic rho zeolite exposed to CH4 have been investigated by electron paramagnetic resonance (EPR) in the temperature range 110-370 K. Depending on the methane adsorption temperature two EPR spectra of oCH3 radicals were recorded. The isotropic quartet observed after CH4 adsorption at room temperature was assigned to oCH3 radicals freely rotating in the middle of octagonal prism. After adsorption at 413 K, the isotropic quartet is overlapped with the second signal characterized with anisotropy of hyperfine splitting and g-value. It is postulated that anisotropic signal represents the oCH3 radicals located in á-cages and strongly interacting with silicaalumina framework. The mechanisms of radiolytic formation of methyl radicals and the possible stabilization sites are also discussed